- vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 40075] GRB 250926A: AstroSat CZTI detection
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42008 SUBJECT: GRB 250926A: AstroSat CZTI detection DATE: 25/09/26 18:53:22 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> A. Goyal (IITB), A. Arya (IITB), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 250926A which was also detected by Fermi/GBM (GCN Circ. 41993). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-09-26 00:21:21.75 UTC. The measured peak count rate associated with the burst is 739 (+163, -167) counts/s above the background in the combined data of all four quadrants, with a total of 396 (+100, -119) counts. The local mean background count rate was 265 (+15, -17) counts/s. Using cumulative rates, we measure a T90 of 1.5 (+0.3, -0.7) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-09-26 00:21:21.04 UTC. The measured peak count rate associated with the burst is 763 (+72, -74) counts/s above the background in the combined data of all quadrants, with a total of 891 (+229, -239) counts. The local mean background count rate was 1162 (+8, -9) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/42008. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40074] GRB 250925A: Swift/UVOT Upper Limits
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42007 SUBJECT: GRB 250925A: Swift/UVOT Upper Limits DATE: 25/09/26 16:33:59 GMT FROM: noelklin(a)umbc.edu N. J. Klingler (NASA-GSFC/UMBC/CRESST II) reports on behalf of the Swift-UVOT team: Swift-UVOT has performed follow-up observations of the Swift-BAT-detected burst GRB 250925A (Dichiara et al. GCN 41985), collecting 6.0 ks of observations between T0+3.74 ks and T0+16.74 ks. No source was detected in the UVOT data at the position of the optical source detected by the Nordic Optical Telescope (NOT) reported by Corcoran et al. (GCN 41990; RA, Dec = 22 44 51.31, +46 33 21.3), which is also consistent with the enhanced position of the X-ray source detected by Swift-XRT reported by Page et al. (GCN 41988; RA, Dec = 22 44 51.30, +46 33 20.6). 3-sigma upper limits (AB) using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: Filter T_start(s) T_stop(s) Exp(s) Mag white 4150.3 4350.1 199.80 >21.55 white 9527.3 10434.5 907.20 >22.41 B 3945.3 5554.0 1608.70 >21.16 U 3739.8 3939.6 199.80 >20.48 U 5175.9 5375.7 199.80 >20.52 V 4560.9 4760.7 199.80 >19.94 V 15320.0 16227.1 907.10 >20.81 W1 4971.0 5170.7 199.70 >20.10 W2 4356.1 4555.9 199.80 >20.10 W2 10440.9 11158.4 717.50 >21.02 M2 4765.8 4965.6 199.80 >19.99 M2 16232.4 16737.3 504.90 >20.67 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.254 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42007. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40073] GRB 250925A: Swift-BAT refined analysis
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42006 SUBJECT: GRB 250925A: Swift-BAT refined analysis DATE: 25/09/26 15:51:01 GMT FROM: Hans Krimm at NSF/NASA-GSFC <hkrimm(a)nsf.gov> S. D. Barthelmy (GSFC), S. Dichiara (PSU), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250925A (trigger #1352124) (Dichiara, et al., GCN Circ. 41985). The BAT ground-calculated position is RA, Dec = 341.207, 46.549 deg which is RA(J2000) = 22h 44m 49.7s Dec(J2000) = +46d 32' 57.0" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 76%. The mask-weighted light curve shows a broad, multi-peaked structure starting at ~T-25 sec and decaying to background by T+50 sec. T90 (15-350 keV) is 64.51 +- 6.59 sec (estimated error including systematics). The time-averaged spectrum from T-23.52 to T+64.42 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.87 +- 0.09. The fluence in the 15-150 keV band is 2.7 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band is 1.2 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1352124 View this GCN Circular online at https://gcn.nasa.gov/circulars/42006. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40072] GRB 250529A: Mondy and AbAO optical observations
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42005 SUBJECT: GRB 250529A: Mondy and AbAO optical observations DATE: 25/09/26 15:27:34 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), R. Ya. Inasaridze (AbAO) report on behalf of GRB-IKI-FuN: We observed the field of GRB 250925A detected by Swift (Dichiara et. al, GCN 41985) at z=3.899 (Castro-Tirado et. al, GCN 41997) with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) and the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations started at Mondy on 2025-09-25 at 20:00 UT, i.e. 0.118 days since trigger. In total we obtained 30x120 s exposures with AZT-33IK, and 85x60 s exposures with AS-32. The optical afterglow initially detected by NOT/ORM (Corcoran et. al, GCN 41990) and also observed by (Saikia et. al, GCN 41986; Pavoni & Moretti et. al, GCN 41989; Bochenek & Perley, GCN 41991; Masi et. al, GCN 41992; Mendez et. al, GCN 41995; Castro-Tirado et. al, GCN 41997; Liu et. al, GCN 41998; Ochi et. al, GCN 41999; Xin et. al., GCN 42002; Rakotondrainibe et. al, GCN 42004) is clearly visible in the stacked images from Mondy. Preliminary photometry is as follows: Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope (nxs) (mid, days) (3sigma) 2025-09-25 20:00:15 6x120 0.12626 R 22.3 0.2 23.1 Mondy/AZT-33IK 2025-09-25 20:12:15 6x120 0.13460 R 22.1 0.2 23.0 Mondy/AZT-33IK 2025-09-25 20:24:16 6x120 0.14294 R 22.1 0.2 23.1 Mondy/AZT-33IK 2025-09-25 20:36:16 6x120 0.15128 R 22.1 0.1 23.1 Mondy/AZT-33IK 2025-09-25 20:48:16 6x120 0.15962 R 22.6 0.2 23.1 Mondy/AZT-33IK 2025-09-25 19:24:44 79x60 0.12486 R n/d n/d 21.7 AbAO/AS-32 The photometry was calibrated against nearby USNO-B1.0 stars (R2-mags) and not corrected for the Galactic extinction. Using all available r-data we estimate a temporal slope of alpha = -1.17 +/- 0.05. View this GCN Circular online at https://gcn.nasa.gov/circulars/42005. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40071] GRB 250925A: COLIBRÍ photometric redshift
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42004 SUBJECT: GRB 250925A: COLIBRÍ photometric redshift DATE: 25/09/26 15:11:23 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> N. A. Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Alan M. Watson (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM): COLIBRÍ performed follow-up observations of the Swift GRB 250925A (Dichiara et al., GCN Circ. 41985, Moreno Méndez et al., GCN Circ. 41995) from 2025-09-26 04:47 to 06:46 UTC (from 11.7 to 13.7 hours after the trigger) and obtained 16/16 minutes of exposure in the g/y filters. We report a detection in the y-filter, with a magnitude of y = 20.64 +/- 0.13 mag and a non-detection of the burst in the g-filter with a 3-sigma upper limit of g > 23.75 mag. The photometry was performed using STDWeb/STDPipe (Karpov 2025), was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. After correcting for the Galactic foreground extinction corresponding to a reddening of E(B-V) = 0.212 mag (Schlafly & Finkbeiner 2011) and fitting a power-law model to the grizy-bands using the LMC extinction curve, we derive a photometric redshift of z = 4.20+0.34-0.52 (1-sigma c.l.), according to the g- and r-band dropouts with g-r > 0.68 mag and r-i ~ 1.45 mag. Our result is consistent with the GTC/OSIRIS+ redshift of z=3.899 (Castro-Tirado et al., GCN Circular 41997). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/42004. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40070] IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42003 SUBJECT: IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/09/26 13:38:42 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 25-09-26 at 12:28:55.17 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_BRONZE alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 3.2659 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/141390_64842455.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 25-09-26 Time: 12:28:55.17 UT RA: 131.0 (+0.56/-0.63 deg 90% PSF containment) J2000 Dec: 9.97 (+0.55/-0.71 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/42003. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40069] GRB 250925A: SVOM/GWAC-F60A upper limit
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42002 SUBJECT: GRB 250925A: SVOM/GWAC-F60A upper limit DATE: 25/09/26 13:10:46 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, X. H. Han, J. Wang, P. P. Zhang, W. L. Dong, H. L. Li, C. WU, Y. L. Qiu, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, L. Lan, W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM follow-up team: We observed the field of GRB 250925A (Dichiara et al., GCN 41985) with the GWAC-F60A at Xinglong Observatory, China. F60A started observing at 2025-09-25T17:05:15 UTC, about 49 sec after the burst. After the image stacking with the exposure time 9*20sec, we do not detected the optical counterpart at the location (Corcoran et al., GCN 41990, Bochenek et al., GCN 41991, Masi et al., GCN 41992,Méndez et al., GCN 41995, Castro-Tirado et al., GCN 41997, Liu et al., GCN 41998) within the XRT error box (Page et al., GCN 41988). The upper limit of R~17.0 mag for GWAC-F60A at mid time of 132 seconds after burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/42002. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40068] GRB 250925A/EP250925a: EP-WXT detection
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42001 SUBJECT: GRB 250925A/EP250925a: EP-WXT detection DATE: 25/09/26 13:07:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou, D. F. Hu (PMO, CAS), Z. H. Yang, Q. C. Zhao (IHEP, CAS), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC) and C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250925a. This transient was found in the ground-processed data, and consistent with GRB250925A in terms of time and space (Dichiara et al., GCN 41985). The start time of EP250925a is around 2025-09-25T17:03:22 UTC. The ground-porcessed WXT location of GRB 250925A is R.A. = 341.205 deg, DEC = 46.564 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic), which is consistent with the localization reported by other groups (Dichiara et al., GCN 41985; Page et al., GCN 41988; Corcoran et al., GCN 41990; Bochenek et al., GCN 41991; Masi et al., GCN 41992; Méndez et al., GCN 41995; Castro-Tirado et al., GCN 41997; Liu et al., GCN 41998). The analysis of the WXT data shows that the event lasted for about 200 seconds with a peak flux of 1.5 x 10^-8 erg/s/cm^2. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.58 x 10^21 cm^-2 and a photon index of 1.18 +/- 0.18. The derived average unabsorbed 0.5-4 keV flux is (5.1 +/- 0.5) x 10^-9 erg/s/cm^2. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/42001. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40067] GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 42000 SUBJECT: GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula DATE: 25/09/26 12:19:19 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Sahil Atri (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250926A detected by Fermi/GBM (Fermi GBM Team GCN Circ. 41993) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-09-26 UTC. DDOTI imaged the GBM error region (Fermi GBM Team, GCN Circ. 41993) from 09:06 to 11:53 UTC (T+8.6 to T+11.5 hours after the trigger), covering the entire region and obtaining a total exposure of 64 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 10-sigma limiting AB magnitude of: w > 20.3 This value is not corrected for Galactic extinction. We note that the Orion Nebula (d ~400 pc) lies within the error region reported by the Fermi/GBM Team. Given the possible association with this nearby star-forming region and the moderate duration of the signal (T90 ~ 5 s), we strongly encourage follow-up observations of this event. Further analysis is ongoing. We thank the staff of the Observatorio Astronómico Nacional at the Sierra de San Pedro Mártir, especially María H. Riesgo Tirado, for their invaluable assistance during the night. View this GCN Circular online at https://gcn.nasa.gov/circulars/42000. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40066] GRB 250925A : MITSuME Akeno optical upper limits
by GCN Circulars 26 Sep '25

26 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41999 SUBJECT: GRB 250925A : MITSuME Akeno optical upper limits DATE: 25/09/26 11:39:31 GMT FROM: ochi.a.21f9(a)m.isct.ac.jp A. Ochi, Y. Kubo, I. Takahashi, R. Kato, H. Hagio, M. Sasada, H. Seki, S. Joshima, Y. Yatsu and N. Kawai (Science Tokyo) report on behalf of the MITSuME collaboration: We observed the field of GRB 250925A detected by Swift/BAT (Dichiara et al. GCN 41985) with the optical three-color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50-cm telescope Akeno. The observation started at 2025-09-25 17:05:14 UT (48 seconds after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any obvious point sources at the position reported by Saikia et al., GCN 41986, Pavoni et al., GCN 41989, Corcoran et al., GCN41990, Bochenek et al., GCN41991, Gianluca et al., GCN41992, Enrique et al., GCN41995, Castro-Tirado et al., GCN41997. We obtained the 5-sigma limits of the stacked images as follows: T0+[s] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 633 | 2025-09-25 17:15:00 | 600 | g'>18.2, Rc>18.1, Ic>17.6 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the trigger T-EXP: Total Exposure time We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; https://github.com/MNiwano/Eclaire) View this GCN Circular online at https://gcn.nasa.gov/circulars/41999. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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